Abstract: A supermarket refrigeration system may include a plurality of supermarket refrigeration cases, each including an evaporator and an associated compressor connected downstream therefrom. A common condenser is connected downstream from the compressors, and a receiver is connected downstream from the common condenser and upstream from the evaporators. A liquid header extends throughout the supermarket and connects the receiver and the evaporators. A discharge header extends throughout the supermarket and connects the compressors to the common condenser. An oil-bearing refrigerant mixture may circulate through a refrigerant circulation path to lubricate the compressors without undesired pooling and without an oil separator. The system may further include a selectively operable defrost circuit which uses hot refrigerant mixture for defrosting.